“A research team comprising members from City University of Hong Kong (CityU), Harvard University and renowned information technologies laboratory Nokia Bell Labs has successfully fabricated a tiny on-chip lithium niobate modulator, an electro-optic modulator which is more efficient, with faster data transmission and lower costs. It is set to revolutionise the industry and CityU researchers are looking into its application for the coming 5G communication.
Electro-optic modulators are critical components in modern communications. They convert high-speed electronic signals in computational devices such as computers to optical signals before transmitting them through optical fibres.
However, the existing and commonly used lithium niobate modulators require a high drive voltage which is significantly higher than that provided by a typical CMOS (complementary metal-oxide-semiconductor) circuitry. Hence an electrical amplifier that makes the whole device bulky, expensive and high energy-consuming is needed.
The electro-optic modulator produced in this breakthrough research is only 1 to 2 cm long and its surface area is about 1/100 the size of traditional ones. It is also highly efficient – transmitting data at rates up to 210 Gbit/second with less energy consumption and about 1/10 optical losses of existing modulators.
The research project, led by Professor Marko Lončar’s research team at Harvard University and titled “Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages”, was published in the highly prestigious journal Nature.
“In the future, we will be able to put the CMOS right next to the modulator, so they can be more integrated, with less power consumption,” said Dr Wang Cheng, Assistant Professor in the Department of Electronic Engineering at CityU and co-first author of the paper.
“The electrical and optical properties of lithium niobate make it the best material for modulator. It is very difficult to fabricate in nanoscale, but we made it with our novel nano fabrication techniques,” Professor Marko Lončar added.
With optical fibres becoming ever more common globally, the size, the performance, the power consumption and the costs of lithium niobate modulators are becoming a bigger factor to consider, especially at a time when the data centres in the information and communications technology (ICT) industry are forecast to be one of the largest electricity users in the world.
This revolutionary invention is now on its way to commercialisation. Dr Wang believes that those who look for modulators with the best performance to transmit data over long distances will be among the first to get in touch with this infrastructure for photonics.
Dr Wang began this research in 2013 when he joined Harvard University as a PhD student at Harvard’s John A. Paulson School of Engineering and Applied Sciences. He recently joined CityU and is looking into its application for the coming 5G communication together with the research team at the State Key Laboratory of Terahertz and Millimeter Waves at CityU.
“Millimetre wave will be used to transmit data in free space, but to and from and within base stations, it can be done in optics, which will be less expensive and less lossy,” he explains. He believes the invention can enable applications in quantum photonics, too.
Professor Marko Lončar and Dr Zhang Mian at Harvard University are the corresponding author and another co-first author of the paper respectively. Other co-authors include Maxime Bertrand and Amirhassan Shams-Ansari from Harvard University, and Chen Xi, Sethumadhavan Chandrasekhar and Peter Winzer from Nokia ell Labs.”